I. Field of the Invention
This invention relates to the generation of electrical power within a downhole drilling motor and, in particular, to power generation utilizing the high speed center precession motion of the rotor in a positive displacement multi-lobed drilling motor.
II. Description of the Prior Art
The multi-lobed drilling motor includes a rotor which is positively displaced within a stator by pumping drilling fluid through the motor thereby driving the downhole drill bit. The rotor moves within the stator in two distinctly different motions, namely "rotation" of the rotor within the stator and "precession" of the rotor center in relation to the axial center of the stator. Still other drilling motors use turbines rotated by drilling fluids pumped downhole to drive the downhole drill bit. In the turbine drilling motors the turbine rotor is aligned with the axis of the housing and rotates about this axis.
Prior attempts have been made to convert the rotational motion of the rotor of these drilling motors into electrical power through a conventional generator associated with the drilling motor. Although electrical power can be generated, the normal motor operating speed is too low to drive an electrical generator capable of powering sophisticated instrumentation. In these prior known drilling motors, the rotor shaft of the drilling motor power section is connected to some type of transmission coupling which in turn is connected to the main shaft of the generator. In at least one known power generation unit the transmission coupling is a non-contact magnetic coupling. Still others utilize direct connection through a solid shaft or universal joints in order to transmit the rotation of the rotor shaft to the shaft of the generator Nevertheless, each of the prior known downhole power generation units suffers from the same fatal flaw of not being capable of generating sufficient rotational speed to drive a generator capable of producing sufficient power levels.